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This tag is for challenges involving matrices. A matrix, also known as a 2D array, is a list of numbers arranged in a rectangle with rows and columns.
1
vote
The Hungry Mouse
J, 82 bytes
g=.](]*{:@[~:])]_1}~[:>./]{~((,-)1 5 6 7)+]i.{:
[:+/[:(g^:_)16,~[:,0,~0,0,0,.~0,.]
Try it online!
I plan to golf this more tomorrow, and perhaps write a more J-ish solution similar to thi …
5
votes
Construct a Modulo Multiplication Table
J, 60 55 bytes
1}."1,/"2@((' ',.' ',":@,.){~(<|.)@(>/~)*1+#|>:*/>:)@i.
Try it online!
-5 thanks to xash
I thought this would be a good challenge for J, and the essence of the problem is, but the form …
9
votes
Drop down the numbers
J, 24 20 bytes
[:>./-@,|."0 2,*,=/]
Try it online!
-4 thanks to xash!
Solved independently, but seems very similar to ovs's APL solution. This one works for any number, because I didn't notice that …
4
votes
Storing a band matrix
J, 66 53 bytes
#{.#|.-@$(#"1~0{](]#~[-:"2*"2)#\>/#\|@-/#\)@|.]{.~3*$
Try it online!
Basic Strategy
We want to avoid special casing the "pad the partial top rows
on the left", and "pad the partial bot …
3
votes
Checkered grid with X mark
J, 40 bytes
((2|+/~)@]+2**@[*=/~@]*(>:]*=/~))|@i:@<:
Try it online!
3
votes
Make the cheapest cut
For example, if the input is a 3 x 4 matrix, the output will be length 5 and should be interpreted as follows:
the first vertical cut is minimal
v
0 0 | 1 0 0
^^^
neither horizontal cut is …
3
votes
Find the box by its corners
The two parts that required the most experimentation to golf were:
(;/-#:i.4)&{ The phrase to pull the 4 corners from a matrix. …
1
vote
Find the representative submatrix
J, 53 bytes
<(0{]#~a:=-.&,&.>)[:(/:#@,@>)@,<<;._3&>~],@{@;&(#\)|:
Try it online!
3
votes
Beware of the matrix tornado!
J, 37 bytes
<./~@g`(|:@|.^:(1<@+>./@g=.#\.<.#\))}
Try it online!
Independently solved, but this approach is very similar to Lynn's.
It is also one of the most perfect problems for J's little used "co …
0
votes
Matrix in Range
.@+:) NB. make the inner part of the matrix
1+i.@+: NB. 1..2*n, where n is the input
(] [\ 1+i.@+:) NB. fork: infixes (sliding window …
3
votes
Reorder a matrix, twice
Main verb ]/:~"1/:
The right most /: sorts the left arg (matrix) according to the order that would sort the right arg (specified order). This sorts rows. …
4
votes
In Flanders Fields
Multiplies by one minus the input, to get rid of endpoints (ie, original crosses)
Add double the original matrix to that. …
5
votes
Dominate a zero-sum game
J, 43 41 40 39 bytes
f=.(#~1=1#.]*/ .>:|:)@~.
f&.:-&.|:@f^:_
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tldr how
Create a function f to filter out dominated rows.
Apply plain f, followed by f "under" a negative transpose, until …
2
votes
Output a Latin Square
Bash, 45 44 bytes
for((i=0;i<$1*$1;)){
echo $[(i/$1+i++)%$1]
}
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-1 thanks to dingledooper
Prints flattened square, one element per line.
2
votes
To raise \$ e \$ to the power of a matrix
J, 31 bytes
[:+/!@i.@99%~]+/ .*^:(<99)[:=#\
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Just implements the formula up to 99 terms, which seems to be good enough to be within 1% of the test cases.